74 



NATURE < >!■ LENTICELS 



majority of plants special devices arc required to bring the 

 living cells of the stem into more direct communication with the 



Fig. 51. Fig. 52. 



Fig. 50. Later development of a lenticel: c, cork cambium; /. intercel- 

 lular space. 



FlG 51. Surface view of lenticels: A, lenticels on branch of horse- 

 chestnut appearing as minute brownish swellings. B, old lenticels on 

 white birch appearing as dark lens-shaped streaks. 



air. This work is effectively accomplished in herbaceous stems 

 by the stomata, bul in stems characterized by the formation of 

 cork it is noticed that the cells just below the stomata begin to 



I 10 53. 1 tion of a stem of castor bean showing the formation 



of the cambium between two vascular bundles: x. xylem; ph, phloem; c, 

 cambium of the bundle. The faint lin< the first divisions of the 



parenchyma cells between the bundles that result in the formation of the 

 cambium 



divide and form a rather Iomm- mass <.f cells that lift Up and 



finally rupture the tissues aboul the stomata, thus forming a 

 small, lens-shaped outgrowth on the surface of tin young stem, 



